Optical recording method and optical recorder

ABSTRACT

A write strategy for use in recording is determined from recommended write strategy parameters recorded on an optical disk ( 160 ) and the characteristics of the optical recording device used in recording; a recommended asymmetry value is determined from the difference between the numerical aperture NA 1  of the objective lens, which is a recording condition of the recommended asymmetry value recorded on the optical disk ( 160 ) and the numerical aperture NA 2  of the objective lens ( 150 ) of the optical recording device used in recording, and recording is carried out on the optical disk ( 160 ) according to the write strategy and asymmetry value thus determined. Optimal recording can be carried out even on an optical disk for which the optimal write strategy information has not been determined in advance, without the need to store write strategy information suitable for each and every optical disk.

FIELD OF THE INVENTION

The present invention relates to an optical recording method and anoptical recording device for recording information on an opticalrecording medium, more particularly to a method of determining the writestrategy to use in recording.

BACKGROUND ART

One example of a conventional optical recording device is a devicehaving a recording and reproducing unit with a strategy section thatcontrols the write strategy for writing to an optical disk, and astrategy information recording unit in which strategy information foroperating the strategy section is recorded; strategy informationcorresponding to device information about the recording and reproducingdevice and medium information about the optical disk is recorded in thestrategy information recording section, read from the strategyinformation recording section, and transferred together with the mediuminformation to the recording and reproducing device. Default strategyinformation is also recorded in the strategy recording section in thisdevice; if strategy information corresponding to the device informationand medium information transferred from the recording and reproducingdevice is not recorded on the storage information recording section, thedefault strategy information is read and transferred to the recordingand reproducing device (see, for example, Patent Document 1).

Patent Document 1: Japanese Patent Application Publication No.2002-56531 (pp. 1-9, FIGS. 1-15)

DISCLOSURE OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

In the above conventional optical recording device, as it is necessaryto first investigate and then store in the optical recording device inthe recording and reproducing device a large amount of strategyinformation corresponding to device information and medium information,much labor was required, and many storage devices such as memory deviceswere needed. Another problem has been that, since the default strategyinformation is used when strategy information corresponding to thedevice information and medium information is not stored in the recordingand reproducing device, there are recording media that cannot berecorded on correctly because of mismatching recording conditions,depending on the optical conditions of the optical disk and the opticalpickup.

The present invention addresses the above problems, a first object beingto obtain an optical recording method and optical recording device thatdo not require the storage of all strategy information suitable forevery optical disk and thus do not require storage devices of largecapacity.

A second object is to obtain an optical recording method and opticalrecording device with which appropriate recording can be carried outeven on an optical disk for which the optimal strategy information hasnot been determined in advance.

MEANS OF SOLUTION OF THE PROBLEMS

The present invention provides an optical recording method comprisingthe steps of:

reading recommended write strategy parameters from an optical recordingmedium on which the recommended write strategy parameters have beenrecorded;

determining a write strategy to be used in recording, based on therecommended write strategy parameters that were read and characteristicsof the optical system of the optical pickup of the optical recordingdevice used in recording; and

writing to the optical recording medium by use of the optical recordingdevice, using the write strategy thus determined.

EFFECT OF THE INVENTION

According to the present invention, given the recommended write strategyparameters recorded on the optical recording medium, an appropriatewrite strategy responsive to the characteristics of the optical systemof the optical pickup of the optical recording device used in recordingcan be determined, and recording can be carried out using the optimalwrite strategy.

A further effect is that it is not necessary to determine theappropriate write strategy for all optical recording mediaexperimentally beforehand, so labor and cost can be saved, and alarge-capacity memory is not required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an optical recording and reproducingdevice in a first embodiment of this invention.

FIG. 2 shows examples of asymmetry values of the reproduced signaldetected in the asymmetry detector in the first embodiment of thisinvention.

FIG. 3 shows examples of write strategies generated in the opticalrecording and reproducing device in the first embodiment of thisinvention when the optical disk is a medium of the dye type.

FIG. 4 is a flowchart illustrating the recording procedure in theoptical recording and reproducing device in the first embodiment of thisinvention.

FIG. 5 is a flowchart for calculating the write strategy fromrecommended write strategy parameters recorded on an optical disk in theoptical recording and reproducing device in the first embodiment of thisinvention.

FIG. 6 illustrates the relationship between the pulse width 1TF and therecommended write strategy parameter ratio 1TP/(1TPˆ2) in the opticalrecording and reproducing device in the first embodiment of thisinvention.

FIG. 7 illustrates the relationship between the pulse width 1TF and therecommended write strategy parameter ratio 2TP/(1TPˆ2) in the opticalrecording and reproducing device in the first embodiment of thisinvention.

FIG. 8 illustrates the relationship between the pulse width 1TF and therecommended write strategy parameter ratio 3TP/(1TPˆ2) in the opticalrecording and reproducing device in the first embodiment of thisinvention.

FIG. 9 illustrates the relationship between the pulse width 1TF and theratio recommended write strategy parameter LTP/(1TPˆ2) in the opticalrecording and reproducing device in the first embodiment of thisinvention.

FIG. 10 illustrates the relationship between the recommended asymmetryvalue β1 recorded on the optical disk and the asymmetry value β2 used inrecording in the first embodiment of this invention.

FIG. 11 illustrates the relationship between jitter value and the writestrategy used in recording in the optical recording and reproducingdevice in the first embodiment of this invention.

EXPLANATION OF REFERENCE CHARACTERS

100 optical recording and reproducing apparatus, 110 semiconductorlaser, 120 laser driver, 130 collimator lens, 140 beam splitter, 150objective lens, 160 optical disk, 170 detecting lens, 180 photodetector,190 head amplifier, 200 data decoder, 210 pre-pit detector, 220asymmetry detector, 230 data encoder, 240 laser waveform controller, 250central controller

BEST MODE OF PRACTICING THE INVENTION

The recording method and recording device in the present inventionrecord information on an optical disk on which recommended writestrategy parameters have been prerecorded. The recommended writestrategy parameters represent a write strategy suitable for use inrecording on the optical disk, and are recorded in the form of pre-pits,for example, in a predetermined area on the optical disk: the lead-inarea, for example.

The optical disk includes, for example, a groove part (not shown)comprising grooves in which information is recorded, and a land part(not shown) between the grooves; the recommended write strategyparameters set by the recording media manufacturer are recorded in theland part together with other information such as an asymmetry value andthe laser wavelength.

The recommended write strategy parameters envision that that recordingwill be performed under predefined conditions. For different recordingconditions, therefore, it is preferable to use a write strategydifferent from the recommended write strategy parameters. According tothe present invention, a write strategy is determined based on therecommended write strategy parameters read from the optical disk, and onthe characteristics of the optical system of the optical pickup of theoptical recording device used in recording, and recording is performedby use of the write strategy thus determined.

First Embodiment

Next, an embodiment of the invention will be described with reference tothe attached drawings.

The optical recording method in the embodiment described below performsrecording (write-once recording) on recording media of the dye type. Theoptical recording method in the embodiment below also performs mark-edgerecording (PWM recording). To record information, based on the data tobe recorded on the optical disk, it causes a semiconductor laser to emitmultiple pulses to form recording marks. In other words, the writestrategy used in the following embodiment is a strategy of themulti-pulse type, having a leading pulse in the mark period, and one ormore multi-pulses following the leading pulse, except in the shortestmark. In the embodiment described below, in a write pulse strategy ofthis multi-pulse type, the pulse width of the leading pulse is changedresponsive to the characteristics of the optical system of the opticalpickup of the optical recording device.

In addition, in the embodiment described below, the recording ofinformation onto the optical disk is carried out by illuminating theoptical disk with optical pulses in patterns corresponding to 3T to 11Tand 14T marks (T being the channel clock period) in EFM modulation.

The longest mark (the mark with length 14T) is a sync pattern.

FIG. 1 shows an example of the basic structure of an optical recordingand reproducing apparatus 100 according to the first embodiment of theinvention. In FIG. 1, the semiconductor laser 110 used as a laser lightsource is driven and controlled by a laser driver 120.

When data are reproduced, a laser beam emitted from the semiconductorlaser 110 with the output value (reproducing power) necessary for datareproduction is focused onto the optical disk 160 through a collimatorlens 130, beam splitter 140, and objective lens 150. The light reflectedfrom the optical disk 160 passes through the objective lens 150, isseparated from the incident light by the beam splitter 140, and is thenreceived through a detecting lens 170 by a photodetector 180.

In the above structure, the semiconductor laser 110, collimator lens130, beam splitter 140, objective lens 150, and detecting lens 170constitute the optical system, which in turn, together with thephotodetector 180, constitutes the optical pickup.

The photodetector 180 converts the optical signal to an electric signal.The electric signal converted by the photodetector 180 is input througha head amplifier 190 into a data decoder 200, a pre-pit detector 210,and an asymmetry detector 220. The data decoder 200 generates(reproduces) the data recorded on the optical disk 160 by performingsuch processes as demodulation and error correction on the inputelectric signal.

From the input electric signal, the pre-pit detector 210 detects pre-pitinformation including such information as the recommended write strategyparameters, which are the recommended parameters of the write strategyto be used for recording on the optical disk 160.

The asymmetry detector 220 couples the input electrical signal by AC(alternating-current) coupling and detects the peak level A1 and bottomlevel A2 of the AC-coupled electrical signal. Using the formula (1)below, it calculates an asymmetry value β from the detected peak levelA1 and bottom level A2.β=(A1+A2)/(A1−A2)   (1)

The peak level A1 and bottom level A2 occur in places where spaces ofmaximum length alternate with marks of maximum length; these values areexpressed with a zero level equal to the average value of the peak leveland bottom level in places where spaces of minimum length and marks ofminimum length appear alternately.

FIG. 2 shows examples of the detection of the asymmetry value in thedetected reproduced signal in the asymmetry detector 220. FIG. 2(a)illustrates the case in which β<0. FIG. 2(b) illustrates the case inwhich β=0. FIG. 2(c) illustrates the case in which β>0.

In the recording of data, a data encoder 230 adds error correctionsymbols to the original data to be recorded and modulates the data togenerate the recording data on which the driving signal to thesemiconductor laser 110 is based. A laser waveform controller 240generates a write strategy signal based on the recording data. Whenprovided with recording data specifying one of 3T to 11T or 14T by acentral controller 250, that is, the laser waveform controller 240outputs a write strategy signal corresponding to the provided recordingdata (a signal having a waveform approximately matching the waveform ofthe emitted optical pulse train).

The laser driver 120 drives the semiconductor laser 110 with the drivingcurrent responsive to the write strategy signal thus generated. A laserbeam emitted from semiconductor laser 110 with the output value(recording power) necessary for recording the data is focused onto theoptical disk 160 through the collimator lens 130, beam splitter 140, andobjective lens 150. Thus, the information is recorded.

FIG. 3 shows an example of a write strategy generated in the laserwaveform controller 240 in the optical recording and reproducingapparatus 100 shown in FIG. 1 when the optical disk 160 is a medium ofthe dye type. FIG. 3(a) shows a channel clock having period T. FIG. 3(b)shows recording data comprising marks and spaces. FIG. 3(c) shows thewrite strategy, i.e., the emitted optical pulse pattern, for recordingthe data in FIG. 3(b). In the emitted optical pulse pattern, the levelis changed between the recording power level and reproducing powerlevel, and the width of each pulse is defined as the period spent at therecording power level.

The shortest mark has a length corresponding to 3T, while the longestmark has a length corresponding to 14T.

FIG. 3(b) and FIG. 3(c) show a case in which the shortest mark isrecorded, then the fourth-shortest mark is recorded.

As shown at the left in FIG. 3(c), when the recorded data are theshortest mark, the write strategy consists only of a leading pulse Fhaving pulse width 1TF.

As shown at the right in FIG. 3(c), recording the fourth shortest mark,the write strategy consists of a leading pulse F having pulse width LTF,followed by three multi-pulses M.

The write strategy recording the n-th shortest mark (4<n<10, having alength corresponding to (n+2)T) consists of a leading pulse F havingpulse width LTF, followed by (n−1) multi-pulses M.

The write strategy recording the longest mark (a mark having length 14T)consists of a leading pulse F having pulse width LTF, followed by elevenmulti-pulses M.

As shown, the marks from the fourth shortest mark to the longest markhave the same leading pulse width LTF.

The write strategy recording the second shortest mark consists of aleading pulse F having pulse width 2TF, followed by one multi-pulse M.

The write strategy recording the third shortest mark consists of theleading pulse having pulse width 3TF, followed by two multi-pulses M.

The width of the multi-pulse M is the same in all of the cases above.

During reproducing and writing operations by the semiconductor laser110, the central controller 250 controls the device as a whole. Thecentral controller 250 receives reproduced data from the data decoder200, pre-pit information from the pre-pit detector 210, and an asymmetryvalue from the asymmetry detector 220, and provides control signals tothe data encoder 230, the laser waveform controller 240, and the laserdriver 120.

In particular, the central controller 250 controls the determination ofthe write strategy, especially the calculation of pulse widths and theasymmetry value, and trial writing performed by use of the modifiedwrite strategy and asymmetry value, as will be described later withreference to FIGS. 4 and 5.

The central controller 250 comprises, for example, a central processingunit (CPU), a program memory such as a read-only memory (ROM), forexample, storing programs for the operation of the CPU, and a datamemory such as a random-access memory (RAM), for example, for storingdata. The program memory stores data representing the characteristics ofthe optical system of the optical pickup of the optical recording andreproducing apparatus 100, a standard numerical aperture NA1, constants(Ki, Ci, Di) for various calculations described later, and a comparisonthreshold value (Δλt). The stored characteristics of the optical systeminclude in particular the wavelength λ2 of the laser beam emitted fromthe semiconductor laser 110, and the numerical aperture NA2 of theobjective lens 150 of the optical pickup. The program stored in theprogram memory specifically includes a section defining formulas fordetermining the write strategy and formulas for determining theasymmetry value, as described later with reference to FIGS. 4 and 5.

It is a general practice to optimize the recording power by performingtrial writing before recording information. The procedure will bedescribed below.

First, trial writing on the optical disk 160 is performed by use of atest pattern comprising 3T-11T spaces and marks corresponding to randomrecording data, for example, under varied recording power; next, thearea on the optical disk 160 on which this test pattern has beenrecorded is reproduced, the asymmetry value is detected by the asymmetrydetector 220, and the detected asymmetry value is compared with a targetasymmetry value in the central controller 250 to obtain the optimalrecording power.

In general, the higher the recording power, the higher the asymmetryvalue, and the lower the recording power, the lower the asymmetry value.

The central controller 250 compares the detected asymmetry valuescorresponding to a plurality of mutually differing recording powers withthe target asymmetry value, and sets the optimal recording power as therecording power that generated a detected value nearest to the targetvalue.

Alternatively, the trial writing on the optical disk 160 may beperformed at one recording power, the data may be reproduced, theasymmetry value may be detected from the reproduced data, the detectedasymmetry value may be compared with the target asymmetry value, and therecording power may be increased or decreased responsive to thecomparison result to find the optimal value.

Within this basic information recording method, in the presentinvention, the pulse width of the leading pulse in the light-emittingwrite strategy for recording is obtained by a calculation based on therecommended write strategy parameters recorded on the optical disk 160and the characteristics of the optical system of the optical pickup ofthe optical recording device used in recording; then the calculatedpulse width is used in recording.

Next, the procedure for the optical recording method of this embodimentwill be described with reference to FIG. 4.

First, when the optical disk to be used in recording is inserted in theoptical recording device, in step S1, the recommended write strategy andrecording condition parameters, i.e., the recommended values iTP (i=1,2, 3, L) of the leading pulse width of the write strategy for recordingeach mark, the recommended asymmetry value β1, and the recommendedwavelength λ1 are read (step S1).

The recommended write strategy parameters include the recommended valueof the leading pulse width of the write strategy for recording eachmark. As the recommended values iTP of the leading pulse width, at leastthe following values are read:

a recommended pulse width 1TP of the leading pulse F for recording theshortest mark;

a recommended pulse width 2TP of the leading pulse F for recording thesecond shortest mark;

a recommended pulse width 3TP of the leading pulse F for recording thethird shortest mark; and

a recommended pulse width LTP of the leading pulse F for recording marksfrom the fourth shortest mark to the longest mark.

The recommended asymmetry value β1 is the target value used to determinethe recording power in the trial writing.

The recommended wavelength λ1 is the laser wavelength under therecording conditions of the recommended write strategy parameters of theoptical disk 160.

Next, in step S2, the write strategy to be used in recording isdetermined based on the recommended write strategy parameters that wereread and the characteristics of the optical system of the optical pickupof the optical recording device used in recording (S2). Details will begiven later.

Next, in step S3, the asymmetry value β2 to be used in recording iscalculated according to the following formula (2), based on thewavelength λ1 read in step S1, the numerical aperture NA1 used fordetermining the recommended write strategy parameter and the recommendedasymmetry value β1, and the numerical aperture NA2 of the objective lens150 of the optical recording and reproducing apparatus 100 used inrecording (S3).β2=β1+E×(NA2−NA1)   (2)

The numerical aperture NA1 is known; data representing the numericalaperture NA1 are prestored in a non-volatile memory comprising ROM, forexample, in the central controller 250. Data representing the numericalaperture NA2 of the objective lens 150, the wavelength β2 of the laserbeam, and the constant E have also been stored in the non-volatilememory in the central controller 250; these data are read and used forthe calculation according to formula (2).

Next, when a recording command is received, trial writing on the opticalrecording medium is performed in step S4, using the write strategyparameters and asymmetry value obtained as above. That is, the writestrategy determined in step S2 is set in the laser waveform controller240, which in turn generates write strategies based on the test patternto perform trial writing to the optical disk 160. At this time, theasymmetry value β2 obtained as above is used as a target value. That is,the optimal recording power is determined by reproducing the area on theoptical disk 160 on which the test pattern has been recorded, comparingthe asymmetry value detected by the asymmetry detector 220 with theasymmetry value β2 calculated in step S3, and performing control to makethe two values match.

Then, after this trial writing has been performed and the power has beenadjusted, the adjusted recording power, the write strategy obtained instep S2, and the asymmetry value calculated in step S3 are used in stepS5 to record data. That is, the write strategy determined in step S2 isset in the laser waveform controller 240, which in turn, generates writestrategies based on the recording data, and performs writing onto theoptical disk 160 with the recording power determined in step S4.

Once the write strategy determined in step S2 has been set in the laserwaveform controller 240 in FIG. 1, when the central controller 250specifies one of 3T to 11T or 14T, a write strategy signal correspondingto the specified value is output from laser waveform controller 240.

FIG. 5 shows the determination process in step S2 in FIG. 4 in moredetail.

First, in step S21 in FIG. 5, from the recommended wavelength λ1obtained in step S1 and the wavelength λ2 of the laser beam emitted bythe semiconductor laser 110 of the optical recording and reproducingapparatus 100, the absolute value of (λ2−λ1) is calculated; if theabsolute value of (λ2−λ1) is less than a predetermined threshold Δλt,such as 3 nm, for example, the process proceeds to steps S22 to S25; ifthe absolute value of (λ2−λ1) is greater than the predeterminedthreshold value Δλt of 3 nm, for example, the process proceeds to stepsS26 to S29.

In step S22, the pulse width 1TF of the leading pulse F for recordingthe shortest mark is calculated from the recommended pulse width 1TPobtained in step S1 and constants K1 and C1, by use of the followingformula (3).1TF=K1×(1TP/1TPˆ2)+C1   (3)

(The notation ‘1TPˆ2’ represents the square of 1TP in thisspecification).

In step S23, the pulse width 2TF of the leading pulse F for recordingthe second shortest mark is calculated from the recommended pulse widths1TP and 2TP obtained in step S1 and constants K2 and C2, by use of thefollowing formula (4).2TF=K2×(2TP/1TPˆ2)+C2   (4)

In step S24, the pulse width 3TF of the leading pulse F for recordingthe third shortest mark is calculated from the recommended pulse widths1TP and 3TP obtained in step S1 and constants K3 and C3, by use of thefollowing formula (5).3TF=K3×(3TP/1TPˆ2)+C3   (5)

In step S25, the pulse width 3TF of the leading pulse F for recordingthe marks from the fourth shortest mark to the longest mark iscalculated from the recommended pulse widths 1TP and LTP obtained instep S1 and constants KL and CL, by use of the following formula (6).LTF=KL×(LTP/1TPˆ2)+CL   (6)

Formulas (3) to (6) can be generalized as follows:iTF=Ki×(iTP/1TPˆ2)+Ci(i=1, 2, 3, L)

In step S26, the pulse width 1TP of the leading pulse F for recordingthe shortest mark is calculated from the recommended pulse width 1TPobtained in step S1 and constants K1, C1, and D1, by use of thefollowing formula (7).1TF=K1×(1TP/1TPˆ2)+C1+D1×|λ2−λ1|  (7)

In step S27, the pulse width 2TF of the leading pulse F for recordingthe second shortest mark is calculated from the recommended pulse widths1TP and 2TP obtained in step S1 and constants K2, C2, and D2, by use ofthe following formula (8).2TF=K2×(2TP/1TPˆ2)+C2+D2×|λ2−λ1|  (8)

In step S28, the pulse width 3TF of the leading pulse F for recordingthe third shortest mark is calculated from the recommended pulse widths1TP and 3TP obtained in step S1 and constants K3, C3 and D3, by use ofthe following formula (9).3TF=K3×(3TP/1TPˆ2)+C3+D3×|λ2−λ1|  (9)

In step S29, the pulse width LTF of the leading pulse F for recordingthe marks from the fourth mark to the longest mark is calculated fromthe recommended pulse widths 1TP and LTP obtained in step S1 andconstants KL, CL and DL, by use of the following formula (10).LTF=KL×(LTP/1TPˆ2)+CL+DL×|λ2−λ1|  (10)

Formulas (7) to (10) can be generalized as follows:iTF=Ki×(iTP/1TPˆ2)+Ci+Di×|λ2−λ1|(i=1, 2, 3, L)

The data representing the constants K1 to KL, C1 to CL, and D1 to DLused in the above steps S22 to S29 are stored in the non-volatile memoryin the central controller 250. These data are read out for use in thecalculations according to formulas (3) to (10).

As stated above, in step S2 the leading pulse widths of the writestrategy used in recording are determined from the leading pulse widthsin the recommended write strategy parameters read from the optical disk.In other words, the recommended write strategy parameters are not usedas is, but are modified. The reason is as follows.

The recommended write strategy parameters, recommended asymmetry value,and laser wavelength are recorded in a predetermined area on the opticaldisk as described above, but when the numerical aperture NA1 of theobjective lens under the recording conditions when the recommended writestrategy parameters were recorded differs from the numerical apertureNA2 of the objective lens 150 of the optical recording and reproducingapparatus 100 used in recording, if the recording power is determined byusing the recorded recommended write strategy parameters and asymmetryvalue, the amount of heat supplied to the optical disk 160 and itsdistribution differ due to the difference in the numerical aperture.Therefore, the size and location of the pits formed corresponding toeach mark length differ, and jitter is worsened. The shift in thelocations at which the pits are formed has a particularly large effecton the jitter. The write strategy is therefore modified or optimized tocompensate for the difference in recording conditions, particularly forthe difference in numerical apertures.

In steps S26 to S29, the pulse widths 1TF, 2TF, 3TF, and LTF of theleading pulse F of the write strategy for recording the shortest mark,the second shortest mark, the third shortest mark, and marks from thefourth shortest mark to the longest mark, respectively, are calculatedby adding values obtained from the formulaDi×|(l2-l1)|(i=1, 2, 3, L)   (11)

This is done to compensate for sensitivity reduction due to wavelengthsensitivity dependence, e.g., the wavelength sensitivity dependence ofthe dye-type medium.

In the above step S3, the asymmetry value β2 used in recording iscalculated in the above step S3 based on the recommended asymmetry valueβ1 read from the optical disk. In other words, the asymmetry value β1recorded on the optical disk is modified before being used. The reasonfor this is as follows.

The difference in the numerical apertures as above causes a differencein the detected asymmetry value. For example, when NA1<NA2, i.e., thenumerical aperture NA2 of the objective lens 150 of the opticalrecording and reproducing apparatus 100 used in recording is greaterthan the numerical aperture NA1 of the objective lens in the recordingconditions under which the recommended asymmetry value was recorded onthe optical disk 160, the asymmetry value detected with an objectivelens having numerical aperture NA2 has a larger value than the asymmetryvalue detected with an objective lens having numerical aperture NA1.Therefore, if recording is performed with an objective lens having anumerical aperture NA2 with a target value equal to the recommendedasymmetry value β1, the detected asymmetry value will have a highervalue than the actual value, due to the difference in the numericalaperture, and recording will be performed with an asymmetry valuesmaller than the recommended asymmetry value β1. Therefore, whenrecording is performed with an objective lens having a numericalaperture NA2, the target is preferably set to a higher value than therecommended asymmetry value β1.

Next, the above procedure will be described in detail. First, theoptimization of the write strategy will be described. It would bepreferable if the correction for optimization could be performed by amathematical formula, but it was not clear what formula to use.

Therefore, the inventors conducted a variety of experiments to findconditions with minimum reproducing jitter, when the recordingconditions of the optical recording device used in recording differ fromthe recording conditions used in determining the recommended writestrategy parameters. One of the experiments performed was directedtoward the relationship between reproducing jitter and the widths of theleading pulses of the write strategy (other conditions being fixed) tofind the leading pulse widths that would minimize reproducing jitter.

As a result, a linear relationship was found between the leading pulsewidth iTF(o) that minimizes reproducing jitter (the pulse width thatminimizes reproducing jitter may also be referred to as the optimalpulse width or optimal value of the pulse width) and the ratio of therecommended pulse width parameter iTP to the square (1TPˆ2) of therecommended leading pulse width parameter of the write strategy forrecording the shortest mark (hereinafter, also referred to as the(iTP/1TPˆ2) ratio or normalized pulse width); from a regression analysisconducted on the data obtained in the experiment, it was found that thisrelationship can be approximated by a line represented by the followingformula (12). The parameters iTP and 1TP are represented as multiples ofthe period of the channel clock. Ki and Ci (i=1, 2, 3, or L) areconstants.iTF(o)=Ki×(iTP/1TPˆ2)+Ci   (12)

Formula (12) can be rewritten as follows.

For the shortest mark, in which i=1,1TF(o)=K1×X1+C1   (13)

For the second shortest mark, in which i=2,2TF(o)=K2×X2+C2   (14)

For the third shortest mark, in which i=3,3TF(o)=K3×X3+C3   (15)

For the fourth shortest mark, in which i=L,LTF(o)=KL×XL+CL   (16)

FIGS. 6 to 9 show lines obtained by the above formulas for the writestrategies used to record the shortest mark, the second shortest mark,the third shortest mark, and the marks from the fourth shortest mark tothe longest mark, respectively.

The slopes Ki and the intercepts on the vertical axis Ci (i=1, 2, 3, L)of the lines shown in the FIGS. 6 to 9 are as follows.

-   -   K1=0.458    -   C1=1.508    -   K2=0.586    -   C2=1.41    -   K3=0.825    -   C3=1.28    -   KL=0.562    -   CL=1.456

In FIGS. 6 to 9, the values of the leading pulse width that minimizedthe reproducing jitter, namely, the optimal values iTF(o) (0=1, 2, 3 orL) of the leading pulse width, are indicated by circles for variousvalues of (iTP/1TPˆ2). As shown in the drawings, the deviation of theoptimal values from the approximation line (the approximation error) issmall.

The experiments from which the results in FIGS. 6 to 8 were obtainedwere conducted under the following conditions. The numerical apertureNA1 of the objective lens in the recording conditions under which therecommended write strategy parameters were recorded on the optical disk160 was 0.60, the numerical aperture NA2 of the objective lens 150 ofthe optical recording and reproducing apparatus 100 used in theexperiments was 0.64, and the wavelength λ2 of the semiconductor laser110 was 657 nm.

As described above, for a particular optical recording device, it wasfound that favorable results can be obtained when the constants are setas above.

The invention is not limited to the above values, however; it is thoughtthat satisfactory results will be obtained if coefficient K1 is set to avalue in the vicinity of 0.46, constant C1 to a value in the vicinity of1.51, coefficient K2 to a value in the vicinity of 0.59, constant C2 toa value in the vicinity of 1.41, coefficient K3 to a value in thevicinity of 0.83, constant C3 to a value in the vicinity of 1.28,coefficient KL to a value in the vicinity of 0.56, and constant CL to avalue in the vicinity of 1.46.

Also as described above, the optimal pulse width (the width of theleading pulse in the write strategy) is affected by the wavelength usedin recording, so if the wavelength of the optical recording devicediffers from the wavelength in the recording conditions under which therecommended write strategy parameters were determined, the wavelengthdifference should be taken into consideration when the pulse widths tobe used in recording are determined. In this embodiment, when thedifference between the wavelengths is greater than a threshold value Δλtsuch as 3 nm, for example, (giving a result of “F” in step S21), acorrection determined according to the wavelength difference is added(steps S26 to S29).

This correction can be determined according to the following formulas(17) to (20).D1×|(λ2−λ1)|  (17)D2×|(λ2−λ1)|  (18)D3×|(λ2−λ1)|  (19)DL×|(λ2−λ1)|  (20)

It was found that, for the particular optical recording device, thecoefficients D1, D2, D3 and DL should all be set to 0.032.

As described above, for a certain optical recording device, it was foundthat favorable results are obtained when the constants D1, D2, D3 and DLare set as above.

The invention is not limited to the above values, however; it is thoughtthat satisfactory results can be obtained by setting the above constantD1 to a value in the vicinity of 0.03, for example.

Furthermore, different values may be used for D1, D2, D3 and DL, insteadof the same value being used as above.

It was also found that when |λ2−λ1| is equal to or less than 3 nm(giving a result of “F” in step S21), the addition operation may beomitted, because 3 nm is within the range of wavelength measurementerror, and because the effect of adding Di×|λ2−λ1| is minor. This is thereason why the addition of Di×|λ2−λ1| is not performed in steps S22 toS25 in FIG. 5.

Next, the modification of the asymmetry value will be described.

As noted above, the optimal asymmetry value is affected by the numericalaperture of the optical recording device used in recording, so when thenumerical aperture of the optical recording device differs from thenumerical aperture in the recording conditions under which therecommended write strategy was determined, the numerical aperture shouldbe taken into account in determining the asymmetry value to be used inrecording. In this embodiment, a correction determined from thedifference between the numerical apertures is added to the recommendedasymmetry value β1 to obtain an asymmetry value β2 to be used inrecording. Specifically, it was found appropriate to use the aboveformula (2).β2=β1+E×(NA2−NA1)   (2)

This is the reason why formula (2) is used in step S3 in FIG. 4.

The triangles in FIG. 10 indicate the values of the asymmetry value β2that minimize the reproducing jitter in a certain optical recording andreproducing apparatus 100 for a plurality of optical disks havingmutually differing recommended asymmetry value β1, and the straight lineindicates the asymmetry value β2 obtained from formula (2) with E=1.493.As shown in FIG. 10, the asymmetry values (optimal asymmetry values)that minimize the reproducing jitter can be linearly approximated by useof formula (2).

As described above, it was found that for a certain optical recordingdevice, good results are obtained if the value of constant E is set asabove.

The invention is not limited to the above values, however; it is thoughtthat satisfactory results will be obtained if the coefficient E is setto a value in the vicinity of 1.5.

FIG. 11 shows reproducing jitter when three pulse patterns were used forrecording on each of ten types of optical disks A to J.

The X marks in FIG. 11 indicate the reproducing jitter when recordingwas performed using the recommended write strategy parameters recordedon each optical disk.

The triangular marks indicate the reproducing jitter when recording wasperformed using the optimized recommended write strategy parametersadjusted so as to obtain optimal reproducing jitter for each opticaldisk.

The circles indicate the reproducing jitter when recording was performedusing the recommended write strategy parameters modified according tothe above formulas (2) to (10).

The constants in formulas (2) to (10) in this case were set as follows:K1=0.458, C1=1.508, K2=0.586, C2=1.41, K3=0.825, C3=1.28, KL=0.562CL=1.456, E=1.493.

In FIG. 11, better reproducing jitter could be obtained on all the diskswhen recording was performed using the corrected recommended writestrategy parameters (as indicated by the circles) than when recordingwas performed using the recommended write strategy parameters recordedon each optical disk (as indicated by the X's). When recording wasperformed using the corrected recommended write strategy parameters (asindicated by the circles), it was possible to obtain nearly the samegood reproducing jitter as when recording was performed using theoptimal write strategy (as indicated by the triangles).

Thus according to the present embodiment, recording can be performedusing optimal write strategies and asymmetry values responsive to thecharacteristics of the optical system of the optical pickup of theoptical recording device.

For example, the optical system conditions such as the numericalaperture and wavelength used in determining the recommended parametersrecorded on an optical recording medium generally differ from theoptical conditions of commercially available optical recording devices,but by taking account of the differences between the specifications of acommercially available optical recording device, particularly thespecifications of the optical system of its optical pickup, and thespecifications of the optical system used in determining the recommendedparameters, it is possible to determine write strategy parameters andasymmetry values suitable for each optical recording device, and toperform recording with write strategies best suitable for each opticalrecording device.

The write strategies and asymmetry values suitable for each recordingdevice can be calculated easily if attention is paid to the differencesbetween optical recording devices, particularly differences in thecharacteristics of the optical systems of their optical pickups, moreparticularly optical system differences including the numericalapertures of their objective lenses, by experimentally determining theconstants (Ki, Ci, Di, E) of the formulas used to determine the writestrategies and asymmetry values, storing these constants in the opticalrecording device, in non-volatile memory in the central control unit,for example, and reading out and using these stored constants inrecording.

The constants only need to be determined once for each type of opticalrecording device or set of specifications; the same constants can beapplied to other optical recording devices of the same type or with thesame specifications. Once constants have been determined for an opticalrecording device of a certain type or with certain specifications, otheroptical recording devices of the same type or with the samespecifications can be shipped with the constants that have beendetermined set therein.

When the specifications of the optical recording and reproducingapparatus 100 are changed, the strategy conditions can be optimizedeasily by selecting or determining the constants (Ki, Ci, Di, E) informulas (2) to (10) again.

In the optical recording method according to the first embodiment,because the recommended write strategy parameters and the recommendedasymmetry value recorded on the optical disk 160 are calculated usingformulas (2) to (10), it is possible to support recording by anyrecording and reproducing device on any recording medium without theneed to store a large amount of strategy information.

Recording can furthermore be performed better than when the recommendedwrite strategy parameters and recommended asymmetry value are usedwithout modification, and nearly as well as when the optimal recommendedoptimal write strategy parameters for each optical disk are used. Goodrecording accordingly can be performed on an optical disk for which theoptimal write strategy information is not known beforehand.

To simplify the calculations, in the above embodiment Di×|λ1−λ2| is notadded when |λ2−λ1| is less than the threshold value Δλt, but when|λ2−λ1| is small, adding it will have little effect on the result, so itmay be added.

Also, the wavelength difference need not be taken into consideration,and the corrections according to formulas (17) to (20) need not beadded.

Furthermore, the correction of the asymmetry value according to thedifference between numerical apertures can be omitted.

In the above embodiment, the pulse width of the leading pulse in thewrite strategy used in recording the fourth shortest mark is also usedin all the write strategies from the write strategy used in recordingthe fifth shortest mark to the write strategy used in recording thelongest mark, but the invention can also be applied when different pulsewidths are set for each mark.

In the above embodiment, in determining the write strategy, the width ofthe leading pulse for recording each mark of the write strategy iscalculated based on the ratio (iTP/1TPˆ2) of the recommended widthparameter (iTP) of the leading pulse for recording each mark (the i-thshortest mark) included in the recommended write strategy parameterswith respect to the square (1TPˆ2) of the recommended width parameter(1TP) of the leading pulse for recording the shortest mark included inthe recommended write strategy parameters. Then the pulse widths of theleading pulses in the write strategy are changed. However, other partsof the write strategy can be changed.

The formulas used for determining the write strategy are not limited toformulas including the above ratio (iTP/1TPˆ2).

1. An optical recording method comprising the steps of: readingrecommended write strategy parameters from an optical recording mediumon which the recommended write strategy parameters have been recorded;determining a write strategy to be used in recording, based on therecommended write strategy parameters that were read and characteristicsof the optical system of the optical pickup of the optical recordingdevice used in recording; and writing to the optical recording medium byuse of the optical recording device, using the write strategy thusdetermined.
 2. The optical recording method of claim 1, wherein: thewrite strategy is a multiple-pulse type of write strategy; and the stepof determining determines a leading pulse width of the write strategyfor recording each mark, based on a ratio of a recommended leading pulsewidth parameter of the write strategy for recording each mark includedin the recommended write strategy parameters with respect to the squareof the recommended leading pulse width parameter of the write strategyfor recording the shortest mark included in the recommended writestrategy parameters.
 3. The optical recording method of claim 2, whereinsaid step of determining is carried out by a computation using a formulapredetermined for the optical recording device used in recording.
 4. Theoptical recording method of claim 3, wherein in regard to the writestrategy for recording each mark of the write strategy, the leadingpulse width that minimizes reproducing jitter is determinedexperimentally, a formula is generated such that the experimentallydetermined leading pulse width is the result of a calculation or a valueapproximating the result of the calculation, and the generated formulais used in said step of determining.
 5. The optical recording method ofclaim 3, wherein the formula is expressed asiTF=Ki·(iTP/1TPˆ2)+Ci (where iTF is the pulse width of the leading pulsein the write strategy to be used in recording an i-th shortest mark, iTPis the pulse width of the leading pulse in the recommended writestrategy parameters for recording the i-th shortest mark, 1TP is thepulse width of the leading pulse in the recommended write strategyparameters for recording the shortest mark, and Ki and Ci are constantsfor determining the write strategy to be used to record the i-thshortest mark).
 6. The optical recording method of claim 3, wherein: thereading step reads the recommended wavelength from the optical recordingmedium; and the formula is expressed asiTF=Ki·(iTP/1TPˆ2)+Ci+Di ×|λ2−λ1| (where iTF is the pulse width of theleading pulse in the write strategy to be used in recording an i-thshortest mark, iTP is the pulse width of the leading pulse in therecommended write strategy parameters for recording the i-th shortestmark, 1TP is the pulse width of the leading pulse in the recommendedwrite strategy parameters for recording the i-th shortest mark, λ2 isthe wavelength of a laser beam of the optical recording device used inrecording, λ1 is a recommended wavelength, and Ki, Ci, and Di areconstants for determining the write strategy to use to record the i-thshortest mark).
 7. The optical recording method of claim 3, wherein: thestep of reading reads the recommended wavelength from the opticalrecording medium; and the formula is expressed as iTF=Ki·(iTP/1TPˆ2)+Ci,when the value of |λ2−λ1| is equal to or less than a predeterminedvalue, and iTF=Ki·(iTP/1TPˆ2)+Ci+Di×|λ2−λ1|, when the value of |λ2−λ1|is greater than the predetermined value, (where iTF is the pulse widthof the leading pulse in the write strategy to be used in recording ani-th shortest mark, iTP is the pulse width of the leading pulse in therecommended write strategy parameters for recording the i-th shortestmark, 1TP is the pulse width of the leading pulse in the recommendedwrite strategy parameters for recording the i-th shortest mark, λ2 isthe wavelength of a laser beam of the optical recording device used inrecording, λ1 is a recommended wavelength, and Ki, Ci, and Di areconstants for determining the write strategy to be used to record thei-th shortest mark).
 8. The optical recording method of claim 6, whereinDi is the same for every i.
 9. The optical recording method of claim 5,wherein the leading pulse width of the write strategy used in recordinga fourth shortest mark is also used in all the write strategies from thewrite strategy used in recording a fifth shortest mark to the writestrategy used in recording a longest mark.
 10. The optical recordingmethod of claim 1, wherein: the step of reading reads a recommendedwavelength value from the optical recording medium; and the step ofdetermining performs a determination based on the recommended wavelengthvalue and the wavelength of a laser beam of the optical recording deviceused in recording.
 11. The optical recording method of claim 1, wherein:the step of recording also reads a recommended asymmetry value; themethod further comprises a step of calculating an asymmetry value foruse in recording based on the recommended asymmetry value and thenumerical aperture of the objective lens of the optical recording deviceused in recording; and the step of writing performs writing by use ofthe calculated asymmetry value.
 12. The optical recording method ofclaim 11, wherein: if the recommended asymmetry value recorded on theoptical recording medium is β1, the numerical aperture of the objectivelens used for determining the recommended value is NA1, and thenumerical aperture of the objective lens of the optical recording deviceused in recording is NA2, then the asymmetry value β2 used in recordingis calculated by the formulaβ2=β1+E×(NA2−NA1).
 13. An optical recording device with an opticalpickup having an optical system for recording and reproducing,comprising: a reading means for reading recommended write strategyparameters from an optical recording medium on which the recommendedwrite strategy parameters have been recorded; a determining means fordetermining a write strategy to be used in recording based on therecommended write strategy parameters that were read and characteristicsof the optical system of the optical pickup; and a writing means forwriting to the optical recording medium, using the write strategy thusdetermined.
 14. The optical recording device of claim 13, wherein: thewrite strategy is a multi-pulse type of strategy; and the determiningmeans calculates a leading pulse width of the write strategy forrecording each mark, based on a ratio of a recommended leading pulsewidth parameter of the write strategy for recording each mark includedin the recommended write strategy parameters with respect to the squareof the recommended leading pulse width parameter of the write strategyfor recording the shortest mark included in the recommended writestrategy parameters.
 15. The optical recording device of claim 14,wherein the determining means carries out a computation using a formulapredetermined for the optical recording device used in recording. 16.The optical recording device of claim 15, wherein, in regard to thewrite strategy for recording each mark of the write strategy, theleading pulse width that minimizes reproducing jitter is determinedexperimentally, a formula is generated such that the experimentallydetermined leading pulse width is the result of a calculation or a valueapproximating the result of the calculation, and the determining meansuses the formula to carry out the calculation.
 17. The optical recordingmethod of claim 7, wherein Di is the same for every i.
 18. The opticalrecording method of claim 6, wherein the leading pulse width of thewrite strategy used in recording a fourth shortest mark is also used inall the write strategies from the write strategy used in recording afifth shortest mark to the write strategy used in recording a longestmark.
 19. The optical recording method of claim 7, wherein the leadingpulse width of the write strategy used in recording a fourth shortestmark is also used in all the write strategies from the write strategyused in recording a fifth shortest mark to the write strategy used inrecording alongest mark.